Improved language detection

[sushain97]

Progress has been made in #73 and apertium/apertium-apy#31

Make language detection work properly and do "did you mean" style if people choose an unlikely source language.

[aditya-prayaga]

Hi @sushain97 I want to work for this issue please tell me where to start!.I was thinking like showing red coloured "did you mean" under the destination Lang textarea div when user clicks Wrong source language.